1. Field of the Invention
The present invention relates to an optical fundus camera having a diopter compensation lens to compensate a diopter scale with respect to a fundus of a subject's eye.
2. Description of the Prior Art
Conventionally, there is known a fundus camera including an illumination optical system for projecting an illumination light to a subject's eye fundus, an observing optical system for guiding the reflected illumination light from the fundus to a first photographing device, and a photographing optical system for guiding the reflected illumination light from the fundus to a second photographing device.
According to Japanese Patent Application Laid Open Nos. 2000-262478 and H9-66032, it is known that such fundus camera includes a stick mirror which may be inserted into or withdrawn from an optical path of the illumination optical system and a focus-target projecting optical system for projecting focus-target light split into two bundles by the stick mirror and the illumination optical system to the fundus.
In such fundus camera, it is determined that the fundus camera is out of focus if two focus-target images formed from the two split bundles of the focus-target light are positioned separately side by side, and the fundus camera is in a focused state if the two focus-target images are lined up vertically.
After a main body of the fundus camera is aligned with respect to the subject's eye fundus, a light-receiving optical system is focused by operations on a focus handle, etc., to shift a focus lens disposed in the light-receiving optical system along an optical axis of the light-receiving optical system.
While in the above described fundus camera, a focusing range of the focus lens is set in a feasible diopter compensation range for a normal person. However, the subject's eye may be of either severe myopia or hyperopia. Thus, it is impossible to conjugate the fundus of the subject's eye with a photographing element even though there are performed focus operations with respect to the fundus of the subject's eye when the subject's eye is of severe myopia or hyperopia.
According to Japanese Patent Application Laid Open No. H7-39523, in order to solve the above problem, there is also known a fundus camera in which diopter compensation lenses enabling a feasible focus of the focus lens are inserted into a light-receiving optical path of an observing and/or a photographing optical system in a case when the subject's eye is of either severe myopia or hyperopia.
However, a subject will not be discovered to be of severe myopia or hyperopia unless it is impossible to have the focus lens focused on the fundus through practical attempts on operating the focus lens while observing the fundus of the subject's eye. And only after that may a diopter compensation lens be manually inserted into the light-receiving optical path. Thus, it costs more time to obtain a photograph for the fundus.